1. Field of the Invention
The present invention generally pertains to the field of heating cables used for personal comfort products such as heating blankets, heating pads, and the like. More specifically, this invention relates to a type of heating cable with a non-heating core-conducting element, and which reduces EMF emissions when a current is passed through the heating cable.
2. Description of the Prior Art
Electric heating cords have been constructed in such a way as to prevent the adverse influence of electromagnetic and electrostatic fields. Prior art has achieved this by utilizing varying methods of insulation under which a heating wire(s) is wrapped around a resistive core material.
In Japanese Patent No. JP404278125A to Itokawa, a first heat generating wire is spirally wound on a core material and covered with a heat resistant insulator. A second heat generating wire is spirally wound on the insulator and covered with a melting layer. This layer is wound with a sensing wire and insulation sheath to form a heat generator. The core material utilized in this heat generator is resistive and thus functions as a heat emitter. By utilizing a resistive core material, the prior art exhibits significant limitations. Namely, there is an approximate 100 Watt limit of operation as well as the possibility of meltdown of the heat generator components when two parallel heating wires are used in this orientation.
Further prior art has utilized conductive core material. For example, U.S. Pat. No. 5,394,507 to Okamoto discloses a plurality of electrically conductive cores wrapped around a tube through which fluid may flow. Said plurality of cores are each covered with an insulator having exposed portions, allowing said cores to contact a tubular braided structure of resistance heating wire. Unlike the present invention, electric current flowing along the conductive cores flows in the same direction along the braided structure of resistance heating wire. Without opposing electric current flow, subsequent opposing electromagnetic fields are not generated, and the reduction of electromagnetic waves is not accomplished by neutralization between the opposing electromagnetic fields.